| 摘要 |
An active filter adapted to filter a line containing an electrical waveform, includes an amplifier, a control system, a waveform measuring device and a coupling circuit. The waveform measuring device, in use, provides an input signal to the control system, the control system controlling the amplifier in response to the input signal and the coupling circuit connecting the amplifier to the system to be filtered. The coupling circuit comprises a passive circuit arranged in a four terminal network of restricted form having no poles in its frequency response within its useful bandwidth. Generally, the four terminal network is provided as a ladder circuit, and a primary use of the filter is to filter ac or dc supplies in electrical power systems.
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